The invention is based on a switched-mode power supply having a power factor correction. A switched-mode power supply of this type has been disclosed in DE 196 10 762 A1.
Switched-mode power supplies produce a severely pulsed load on the line network, which leads to harmonic currents on the line network. This load occurs in particular at the voltage peaks of the sinusoidal network voltage, at which points an energy-storage capacitor in the switched-mode power supply is recharged. In order to limit this load from harmonic currents, an increasing number of international regulations are being produced for switched-mode power supplies whose aim is to design future switched-mode power supplies to achieve a more sinusoidal current consumption. The harmonic load on the line network can also be quoted in terms of a so-called power factor.
Another switched-mode power supply with a reduced harmonic load on the line network is disclosed in EP 0 700 145 A2. This switched-mode power supply likewise contains a second current path on the primary side, which has an inductance and a diode and produces a connection between a charge capacitor downstream of the rectifier on the network side and a tap on the primary winding of the transformer. The inductance acts as an energy store which is charged in the phase when the switching transistor is switched on and subsequently emits its energy, in the phase when the switching transistor is switched off, via the diode and the primary winding to the energy-storage capacitor. This charging and discharging process leads to a current drawn from the line network over the entire 360.degree. phase range of the line network, since an unfiltered half-wave sinusoidal voltage of constant polarity is present across the charging capacitor.
EP 0 598 197 A2 discloses a switched-mode power supply having a sinusoidal current consumption, which contains a current pump with a capacitor which is charged via the network rectifier during the phase when the switching transistor is switched on, and emits this stored energy to an energy-storage capacitor when the switching transistor is switched off.
The object of the present invention is to specify a switched-mode power supply of the type mentioned initially, which operates reliably over a wide input voltage range.